Internet Service Providers (ISPs) are highly desirous of providing Internet Protocol (IP) services, such as Voice over IP (VoIP) and IPTV, to their customers. In order to provide these high value services, the ISP networks need to provide a high Quality of Service (QoS) even as their networks become more complex. There is, therefore, an increased demand for sophisticated monitoring tools that allow the ISPs to rapidly identify degradation in their networks performance and quickly isolate the root cause of any problems. Such tools are critical for ensuring QoS guarantees and for reducing service downtimes through timely resolution of network problems. These monitoring tools typically monitor network traffic parameters such as delay and packet loss using either active or passive measurements.
Active monitoring tools typically inject data packets into the network, or send data packets to applications, in order to obtain measurements of delays or losses.
Passive monitoring devices, in contrast, snoop on existing data-packets as they traverse the network lines as normal network traffic. Passive monitoring has the advantage that it does not increase the traffic in the network. This can be critical when a network interface or link becomes congested. During such times, injecting additional traffic into the network for active measurements may exacerbate the very problem that is being diagnosed. The disadvantages of passive measurements, however, include having less control over the measurement process as only existing network traffic is used and that the amount of data that needs to be collected can be enormous.
In order to control the costs of a passive monitoring infrastructure and the communication overhead between the monitors and the Network Operations Center (NOC), it is important to carefully select the locations at which passive monitoring probes are placed and the paths they are used to monitor. At the same time, it is important to ensure that the data collected by the monitoring probes is sufficient to provide a comprehensive and timely overview of the network's performance. In particular, it is important to provide enough passive monitoring locations that both a detection set of paths and a diagnostic set of paths can be monitored. A detection set of paths for passive monitoring of a communications network is the minimum set of paths that need to be monitored in order to detect that there is an anomaly somewhere in the network. A diagnostic set of paths is the minimum set of paths that need to be monitored in order to accurately locate and diagnose any anomaly that occurs anywhere in the network.